(1) Field of the Invention
The present invention relates to a process for the preparation of hydrous silicic acid to be used as a filler for paper.
(2) Description of the Related Art
Recently, the basis weight of paper has decreased, but if the basis weight of paper is decreased, the opacity is undesirably reduced upon printing. As a means of preventing this reduction of the opacity of paper after printing, there is ordinarily adopted a method in which a filler is added to the paper. Various inorganic and organic fillers have been proposed and developed, but even at the present, a cheap filler having satisfactory effects is not available. Furthermore, not only a prevention of a reduction of the opacity after printing but also an improvement of the quality of the printed surface, especially the ink receptivity, is now strongly desired.
Among various fillers, a silicic acid filler is cheaper and has higher effect of imparting opacity upon printing. However, the effect of this filler is not high because of an unsatisfactory retention thereof in the paper and a reduced ink receptivity of the paper.
A process for the preparation of hydrous silicic acid preferred as a paper filler and a process for the preparation of a hydrous silicic acid slurry for preventing a print-through of the paper are disclosed in Japanese Examined Patent Publications No. 49-36877, No. 52-28754, and No. 52-28755, and Japanese Unexamined Patent Publication No. 55-113611. However, when paper is manufactured from a pulp slurry in which a product prepared by the known process as mentioned above is incorporated, the filler is dislodged during the papermaking operation and is deposited on a meter of a paper machine such as a moisture meter or a caliper, and when the formed paper is printed, the filler is dislodged and adheres to a printing plate of a printer and has a fatal defect of shortening the life of the printing plate. Furthermore, the above-mentioned filler is not capable of improving the ink receptivity of the paper.